140 Darwin and Romanes dealt witli. 



followers is, as it would have been for him, had he 

 still been with us, to tell why the gift of detection 

 has been so clearly conferred on some birds, that 

 they will not receive a cuckoo's egg at all. If in- 

 stinct suffices for tnem, why not for all the others ? 

 though their own interests, and the increase and con- 

 tinuation of their own species, were clearly threatened 

 by it. And yet Mr. Romanes contents himself with 

 saying that, except as regards the question of some 

 voluntary power of colouration of eggs, there is 

 nothing connected with these instincts of the cuckoo 

 and duped birds that presents any difficulty to the 

 theory of evolution. If not to it, they most certainly 

 did to him ; and that he did not see or feel it is ex- 

 actly our point proved. 



XVII. 



If the cuckoo lays a larger number of eggs than is 

 generally supposed, as both Dr. Rey and I believe — 

 though I do not tie myself to Dr. Rey's number, and 

 if I may draw any inference from the immense number 

 of cuckoos in the area with which I am best acquainted, 

 then it is beyond all things clear that " the deposition 

 of a parasitic egg " is far from being " comparatively 

 an exceedingly rare event : " eggs having been found 

 by me in nests which it is not generally thought that 

 the cuckoo at all has resource to — in the nests of 

 starlings, thrushes, linnets and larks — (on the ground, 

 mark you, where the throwing out would be difficult) 

 and bullfinches, namely. Whatever errors the indi- 

 vidual cuckoos may be guilty of, or whatever necessity 



